// Copyright (C) 2017 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package protoutil

import (
	"reflect"
)

// OneOf returns the value of a oneof proto field.
// For example, given the proto:
//
//   message M {
//     oneof o {
//       A a = 1;
//       B b = 2;
//       C c = 3;
//     }
//   }
//
// OneOf(m.o) will return either a, b, c or nil, skipping the wrapper struct.
func OneOf(v interface{}) interface{} {
	if v == nil {
		return nil
	}
	return reflect.ValueOf(v).Elem().Field(0).Interface()
}
